The flaw affects Struts 2.3 through 2.3.34, Struts 2.5 through 2.5.16, and possibly unsupported versions of the framework.

Tracked as CVE-2018-11776, the bug is rather trivial to exploit: because Apache Struts doesn’t properly validate namespace input data, an attacker would only need to insert their own namespace as a parameter in an HTTP request.

Neither the Apache Software Foundation – which announced the availability of patches on August 22 – nor Semmle – the code analysis company that reported the bug in April – provided technical details, but a proof-of-concept (PoC) exploit for the vulnerability was published within days.

Now, Volexity says they have observed the first malicious campaign targeting the vulnerability. The attacks apparently started shortly after the PoC was released.

“Volexity has observed at least one threat actor attempting to exploit CVE-2018-11776 en masse in order to install the CNRig cryptocurrency miner. The initial observed scanning originated from the Russian and French IP addresses 95.161.225.94 and 167.114.171.27,” the security firm reveals.

The observed exploit attempts to retrieve a copy of CNRig Miner from Github (saves it as xrig) and a shell script from BitBucket by performing wget requests to the URLs the two pieces of code reside at.

Among other actions, the shell script removes specific processes, deletes previous instances of the miner, and downloads three ELF cryptomining binaries. These are miner executables targeting Intel, ARM, and MIPS architectures, which shows the broad scope of the attack.

“[I]t shows the miner is capable of running across a wide range of hardware, such as servers, desktops, laptops, IOT devices, wireless routers, and more — nearly any internet connected device running a vulnerable instance of Apache Struts,” Volexity points out.

The BitBucket folder appears to be an open directory that contains both the shell script and the ELF binaries. Mining account name is the same as the BitBucket account name, the security firm says.

Apache Struts framework’s popularity makes it a highly appealing target to cybercriminals and threat actors alike, and it’s no surprise that the recently addressed bug is already being abused for malicious purposes.

A Critical remote code execution flaw addressed in the framework in March 2017 was still being targeted one year later, SANS Internet Storm Center handler Guy Bruneau reported several months ago.